Hi Roger-

The problem you are describing sounds very much like a power issue on that line. Is that a long cable run?
If it is longer than 180 feet, you might be experiencing voltage drop on that line. This is magnified at night when the IR LEDs come on. (Voltage drop increases as the load increases)
Have you tried swapping a known good camera to that cable? That is the best way to troubleshoot the cable and power. Sounds like you have isolated the issue to that particular cable/camera - now the last step is to determine if it's the cable or the camera. Swapping it with a known good camera is the best way to sort that out. That will also show if that camera is good on a different line. That would be my first suggestion to troubleshoot it.

Roger -

It looks like cable length is not an issue then. It could be interference though - are there any high power lines close to your cable run? (Or anything that would emit RF interference, like high power motors, flourescent lighting ballasts, or microwave or anything like that?)

As for the 15V power supply - definitely a 'no go' unless you have really long cable runs - enough to produce a 3V drop in the cable. That 15 V on a short cable is enough to burn up the camera. If that was the same camera - then it still points to a low power condition - the higher voltage was enough to get it fully powered - but that is obviously not an option for the long term.

I hate to say it, but I think swapping that camera for a known working camera is the only good test to isolate whether it's a cable or camera problem. If swapping the cable itself is somehow easier - that's worth a try, but it leaves open the possibility of a routing issue where the new cable could be subject to the same RF interference. (if RF is the issue) That would make it appear to be the camera, because you swapped to a new cable - but if it's RF, the new cable would act the same. That's why i say the only definitive test would be to swap a known working camera to that position= if it also messes up, then there is an environmental issue pointing to the cable, or rarely, there may be high RFI at the camera mount position. (That's usually pretty unlikely)

The only other good test is to pull that camera down and test it on a short cable. (6 or 10 foot) If it tests good on a short cable...once again that would point to a cable issue.

Sorry I can't think of an easier way to test that doesn't involve taking the camera down.

Roger -

The 110V line could well be causing interference if they are running parallel for that distance. A good rule of thumb for separation would be to keep them 8 ~ 12 inches apart at minimum if possible. (Crossing a high power line at right angles does not affect you as much as running parallel) If the camera is 3 years old and this problem has just started - the camera itself may be producing a weaker signal now, and just starting to allow the interference to affect it. (All electronics degrade over time with use) If possible - see if you can get some more separation in that 15~20 foot run. That may be our culprit.

As for the 12VDC line burning the cable in half - I am guessing it was siamese cable (coax with the 12 volt lines attached as a seperate cable) Did that burn through the coax as well, or just the 12VDC part? I have been in this industry for 14 years now and have never heard of that happening. Usually the 12VDC is fused or has thermal breakers in the supply side that should have killed the connection before it gets that hot. (referring to a 12VDC power box where all cameras connect to same power supply) If you were using 'wall warts' they may not have that same protection though. Rest assured that is a pretty rare occurence for a 12VDC  line in any case.

Roger,

What is the possibility that a critter may have chewed the wire? That's pretty uncommon for a siamese to burn through for no reason.

Especially from a 12 VDC power supply. Your wall warts should be 12 VDC with a minimum of 1 Amp for each camera.

The best protection against any overheating would be to use a power supply that has internal fuses or thermal breakers. Most professional power supplies have that. It also makes for a lot cleaner installation to have a single power supply instead of all those wall warts. here is an example of a 16 channel supply = http://www.securitycameraking......-prd1.html

Ha ha! I've seen those little beasts with flaming teeth! What I was thinking was something gnawed on the line just enough to break the insulation and cause a short - then the current would have taken over and melted the line. (still pretty far fetched idea) I was thinking another possibility is a lightning strike - where the lightning chose that point to exit the line and jump to something nearby that was grounded. Seems like you would be able to find burns on something else close by if that were the case.

When I say siamese cable - that is generally a standard coax cable (RG-59 or RG-6) with an 18/2 conducter attached to the outside of it. They are not molded inside the same insulation, but just attached - that way you can pull them apart at each end to get to the two different end points of power and video. At the DVR end you would split them apart several feet - run the 18/2 to the power source and the coax to the DVR.

As for testing - the only sure test is to disconnect the cables from camera and DVR - (have them connected to nothing)- then run a continuity test - there should be no connection between any of the 4 leads (coax center line / coax ground / 12V + / 12V -)
Now - I have assumed that you are running coax or siamese cable because you mentioned BNC connectors - but you mentioned the wiring earlier and it gave me the impression you may be using Cat-5 with baluns at each end. (Cat-5 is network cable with 8 wires inside it twisted into 4 pairs) That kind of wire could be burned through a LOT easier than siamese. Wires are thinner and there is a lot more possibilty of something shorting due to defective insulation.

And then the power supply - yes it has screw terminals for power output. (+ and - for each camera) That is where you would just pull a siamese cable apart - the 18/2 would run directly to the power supply - no ends needed - just screw them down, and the coax goes to the DVR and attaches with BNC connector.

At any rate - having a line burn like that is not just uncommon, it is a little odd! I would think the possibility of that happening again are fairly astronomical.